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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Agricultural and Biosystems Engineering

First Advisor

Daniel S. Humburg


Pulse width modulation (PWM) technology has recently been applied to chemical injection systems. However, its impact on the performance of sprayers is not well understood. Although the behavior of chemical injection systems in constant-rate application has been studied intensively, little research has been documented on how control systems impact sprayer performancein the context of variable-rate application.
A pulse width modulation (PWM) carrier control sub-system for a chemical application system was modeled mathematically. A control algorithm was implemented which had a step response with a time constant of 0.7 seconds. For simulation purposes, the PWM carrier control test system was conceptually incorporated with a Raven SCS- 700 chemical injection system in a model of a sprayer. A computer simulation was developed using the PWM carrier control model developed in this paper and the chemical control model developed by Steward (1994). Three types of sprayers were simulated; a conventional boom-broadcast sprayer used by private applicators, a conventional boom broadcast sprayer used by commercial applicators, and a band sprayer with conventional plumbing used by private applicators. Three strategies for carrier control were compared. PWM carrier control with a predictive algorithm had better system performance than PWM carrier control with a PID algorithm and pressure-based carrier control with a proportional algorithm. Chemical injection systems with carrier control represent a superior strategy when compared to systems without carrier control for overcoming the problem of transport delay. The performance of the three types of sprayers was simulated under conditions of site-specific chemical application. Again, PWM carrier control with a predictive algorithm gave the best overall performance.

Library of Congress Subject Headings

agricultural chemicals application
mathematical models
agricultural chemicals application
computer simulation
spraying equipment
spraying and dusting in agriculture


Includes bibliographical references (140-143)



Number of Pages



South Dakota State University


Copyright © 1998 Xiao Chen. All rights reserved